1. Technical Field
The present invention relates to a serial-type printer used with a rolled sheet in which printing is performed on a rolled sheet while a printing head is moved in a width direction of the printer, and more particularly, to an improved technique for downsizing the printer.
2. Related Art
A serial type printer using a rolled sheet is known for issuing a receipt or the like, wherein the performs printing while a printing head mounted on a carriage is moved in a lateral direction of the rolled sheet. Generally, in the printer of this type, the rolled sheet is accommodated so as to extend in the lateral direction horizontally, and printing is performed on an elongated sheet drawn out from the rolled sheet while reciprocally moving the carriage mounting the printing head in the lateral direction.
In this structure, a moving range of the carriage which carries the printing head, that is, the moving range of the carriage required for performing one line of printing is larger in the lateral direction, as compared with a dimension of the rolled sheet in the lateral direction. Therefore, it is necessary to provide a space having a laterally larger width than a rolled sheet chamber, as a moving space for the carriage. For this reason, a dimension of the printer in the lateral direction depends on the moving space of the carriage, and a dead space is formed at one or both sides of the rolled sheet chamber in the lateral direction of the printer. This dead space is an obstacle when the serial-type printer is intended to be downsized.
In the serial-type printer in which an ink jet head is employed as the printing head, a DC motor is sometimes used as a motor for moving the carriage on which the ink jet head is mounted. In this case, a linear scale is provided along a moving path of the carriage for the purpose of detecting a rotation direction and a rotation position of the DC motor, that is, a moving position of the carriage. For example, in case of an optical linear scale, the linear scale is provided with a plurality of slits, and a photo sensor mounted on the carriage reads the slits, whereby an A-phase signal and a B-phase signal which are shifted, for example, by 90 degrees are generated. According to such detection signals, rotary conditions such as the rotating direction and the rotation speed of the DC motor (the moving direction and the moving speed of the carriage) are detected. The DC motor is feedback controlled according to the results of the detection, so that the movement of the ink jet head which is mounted on the carriage can be controlled.
On this occasion, a part of an ink drop which is ejected from the ink jet head to the recording sheet floats as minute ink mist. Moreover, a nozzle face of the ink jet head is opposed to the recording sheet keeping a narrow gap. Consequently, when the carriage which carries the ink jet head reciprocally moves, a negative pressure is created in the gap, and a part of the ink drop is blown off to generate the ink mist. The generated ink mist flies on an air stream which is created with the movement of the carriage and is scattered around, so that surfaces of components around the carriage may be soiled. Particularly, where the air stream created with the movement of the carriage flows in a direction perpendicular to the moving direction of the carriage, there is a concern that a surface of the linear scale which is arranged near the carriage along the moving path of the carriage may be soiled with the ink mist, which will hinder normal position detecting operation.
In order to avoid this concern, in Japanese Patent Publication No. 11-138781A (JP-A-11-138781), a blowing fan is arranged near the moving path of the carriage to create an air stream flowing in the moving direction of the carriage so that the ink mist may not run toward the linear scale. In Japanese Patent Publication No. 2001-138548A (JP-A-2001-138548), wind guide plates are arranged so as to create an air stream by a moving force of a printing head, and the ink mist is ejected by the air stream. In Japanese Patent Publication No. 2005-88235A (JP-A-2005-88235), a regulating rib is provided on a surface of the carriage to regulate an air stream created with the movement of the carriage so that the air stream will not run toward the linear scale behind the carriage.
In the small-size rolled sheet printer which issues a receipt or the like, there is only a small space for moving the ink jet head. Accordingly, it is impossible, in many cases, to secure a space for installing the blowing fan which will create the air stream, a space for installing the wind guide plates, or a space for moving the carriage having the regulating rib formed on the surface. Therefore, incorporation of a mechanism for preventing deposition of the ink mist on the linear scale has been a problem, particularly when the rolled sheet printer of the serial type is intended to be downsized.